Data transmission line receivers for use in EIA RS422/423 applications are well known. Typically, a line receiver is operated from a single power supply to receive the transmission of digital data on a differential, balanced twisted-pair transmission line. The line receiver generally includes a differential amplifier having a pair of inputs coupled to inputs of the line receiver through an attenuation circuit.
A problem can arise, due to input signal failure, which may cause the output of the line receiver to oscillate. This is undesirable because the oscillations may be treated by the end user equipment which is connected with the line receiver as digital data to create erroneous information. The signal failure may happen, for example, by the input to the line receiver being either open or short circuited.
Hence, there arises a need for providing a fail safe circuit which can guarantee that the output of the line receiver will go to a predetermined output state if the input thereof is either open or short circuited to thereby inhibit oscillations at the output of the receiver.
In addition, it is desirable to provide a fail safe circuit which allows the use of a termination resistance for matching of the receiver to the transmission line while providing the aforementioned fail safe feature.